The present invention relates to a multipole commutator motor having at least four stator poles and having armature coils that work together with these stator poles. In order to supply power, the armature coils are each connected electrically to two commutator bars of a commutator. The number of armature coils is greater than the number of stator poles; in order to reduce the number of brushes contacting the commutator, armature coils that form armature poles having the same magnetic orientation are connected in parallel by electrical bridge conductors at the armature.
Commutator motors of this sort are used for example as pump drives for anti-lock braking systems in motor vehicles, as servo drives, or as adjusting drives. Commutator motors of this sort can also be referred to as small-power motors, because they standardly cover a power range up to approximately 1 kW.
A typical example of a commutator motor of this sort has for example four stator poles that are preferably permanently excited, and correspondingly has four armature poles that work together with these stator poles and that are formed by armature coils. The armature coils are connected to a commutator at the armature, which commutator is standardly provided with current via four brushes. The brushes slide over commutator bars of the commutator.
In order to save brushes, in the prior art it is known to connect armature coils that form magnetically identically oriented armature poles in parallel, using electrical bridge conductors at the armature. For this purpose, German letters patent DE 197 57 279 C1 proposes that the bridge conductors be formed as commutator bar contact bridges, formed by winding wire and wound on during the winding of the armature coils. Like the armature coils, the bridge conductors are suspended in hooks that are situated on the commutator bars, facing the armature coils. The suspension of the armature coils is unproblematic, because the armature coils extend essentially in the direction of the axis of rotation of the armature, and can thus easily be placed in the hooks. In contrast, the suspension of the bridge conductors is problematic, because these must extend transverse to the direction of the axis of rotation of the armature, because, typically, commutator bars situated diametrally opposite one another are connected with one another by the bridge conductors. In addition, it is necessary to provide an electrically insulated segment on the shaft of the armature in order to support the bridge conductors.
In high-power commutator motors, or those having a power output significantly greater than one kilowatt, commutator bars are connected in parallel by equalizing connections in order to enable equalizing currents to flow between the commutator bars, so that the brushes are not loaded by equalizing currents. However, a reduction of brushes is not provided, and would lead to high commutator currents in such high-power motors, which would result in a problematic current chopping behavior, and possibly even flashing at the commutator.
Advantages of the Invention
In contrast, in the multipole commutator motor according to the present invention the bridge conductors are routed via armature slots, so that xe2x80x9csuspension anglesxe2x80x9d on the commutator bars are possible that are advantageous from the point of view of winding. In the area of their connectionxe2x80x94by suspension, soldering, or otherwisexe2x80x94with the commutator bars, the bridge conductors extend essentially along the axis of rotation of the armature, whereas in the prior art they extend transverse to the direction of the axis of rotation in this area. Thus, the present invention significantly simplifies the winding of the armature. In addition, the commutator motor is of compact construction, because no space need be provided between the commutator and the armature teeth for bridge conductors that may have to be situated there. In any case, the provision of the bridge conductors saves brushes, so that the commutator motor according to the present invention can be manufactured economically.
Through the measures stated in the subclaims, advantageous developments and improvements of the inventive commutator motor are possible.
The bridge conductors are each preferably wound around at least two or more armature teeth. Here, it has proved advantageous to manufacture the bridge conductors from winding wire and to suspend them together with the armature coils on the suspension devices provided on the commutator bars for the suspension of the armature coils. Of course, other types of connection are also possible for the electrical connection of the bridge conductors with commutator bars, e.g. soldering, crimping, or welding.
Bridge conductors formed from winding wire can advantageously be wound on immediately during the winding of the armature coils. They are then usefully made of the same winding wire as the armature coils, so that no change of material is required during the installation of the bridge conductors.
In principle, the bridge conductors can be formed from a single electrical conductor, e.g. a single winding wire, of which in each case one end is connected electrically with a commutator bar. This variant of the present invention has proved advantageous in practice.
However, it is also possible to form the bridge conductors from a plurality of line connections, e.g. from two line connections. In this variant, it is possible for the line connections allocated to a bridge conductor to be routed via different armature slots. On the one hand, in this way the current loading of the individual line connections of a bridge conductor is reduced, and on the other hand it is possible, in an advantageous construction of the present invention, for the line connections that are respectively allocated to a bridge conductor to be situated together with the armature coils in the armature slots in such a way that a flow of current is possible that is oriented in the same direction on the respective armature coils and on at least one line connection situated in common in an armature slot. The flow of current oriented in the same direction prevents a weakening of the field of the respective armature coil.
It is advantageously provided that commutator bars situated diametrally opposite one another on the perimeter of the commutator are connected in parallel by a respective bridge conductor. This variant is especially advantageous in the case of a four-pole commutator motor. However, it is of course also possible for commutator motors having more than four poles, e.g. having six or eight poles, to be equipped with the bridge conductors according to the present invention.
Advantageously, supports and/or fixing devices are provided for the holding of the bridge conductors, so that the respective bridge conductors are electrically insulated from an armature shaft that penetrates the armature of the commutator motor. In addition, the supports or fixing devices mechanically stabilize the bridge conductors.
However, the bridge conductors can also advantageously be mechanically fixed by an insulating compound, in particular a casting compound.
In principle, the armature coils can be applied on the armature in various winding variants. In practice, a multipole lap winding has proved advantageous.
A preferred area of application for the present invention is the area of electrical small-power motors, up to a power range of one kilowatt, as are used for example as a pump drive of an antiblocking system for motor vehicles, as a servo drive, or as an adjustable drive.